A frame transfer CCD image sensor in general include three parts: a photosensing array, known as the A-register; a temporary storage array, known as the B-register; and an output register, known as the C-register. In one type of CCD image sensor the A-register includes a plurality of spaced, parallel buried-channel regions in the form of regions of N- type conductivity formed in a substrate of single crystalline silicon of P- type conductivity and extending along a surface of the substrate. A plurality of parallel gates of a conductive material, such as conductive polycrystalline silicon, extends transversely across the channels and are insulated from the surface of the substrate by a layer of silicon oxide. The B-register likewise includes a plurality of spaced, parallel buried-channels which are extensions of the channels of the A-register. A plurality of spaced, parallel conductive gates extend transversely the channels of the B-register. The C-register includes a single buried channel extending across the ends of the B-register channels and a plurality of conductive gates extending transversely across the channel. The A-register and the B-register include channel stops extending between the channels to isolate the channels. The A-register can also include blooming drains between the channels. Such blooming drains are disclosed in U.S. Pat. No. 4,362,575 to L. F. Wallace, issued Dec. 7, 1982 entitled "Method of Making a Buried-Channel Charge-Coupled Devices With Means For Controlling Excess Charge" and the patent application of E. D. Savoye et al., Ser. No. 455,332, filed Jan. 3, 1983 entitled "Imaging Array Having High Sensitivity And Method of Making The Same", and assigned to the same assignee as the present application.
There are some uses for CCD image sensors, such as for surveillance in space or high resolution television imaging, which require the use of a plurality of the image sensors mounted in side-by-side abutting relation so as to be capable of sensing a large area. For such a use, it is desirable that the edge of a substrate be as close as possible to the sides of the A-register, the CCD sensing area, so that when the sensors are mounted together the A-registers of the various sensors will be as close as possible to minimize dead space between the individual sensors. However, it has been found that charge carriers are generated at the edges of the substrate, and, if these charge carriers are injected into the CCD channels, they introduce a fixed pattern noise and may overload the CCD register, thereby adversely affecting the image being detected. Therefore, it is desirable to passivate the edges of the substrate to prevent injection of the undesirable charge carriers into the CCD registers. A type of high resolution CCD imager where this problem can exist is described in the patent application of Hammam Elabd et al., Ser. No. 590,888, filed Mar. 16, 1984 entitled HIGH RESOLUTION CCD IMAGERS, and assigned to the same assignee as the present application.